1. Field of the Invention
The present invention relates to a recovery type steam-cooled gas turbine in which supply steam for cooling is prevented from leaking.
2. Description of the Prior Art
FIG. 3 is a cross sectional view of a gas turbine which employs a representative steam-cooled system in the prior art. In FIG. 3, numeral 50 designates a compressor and numeral 51 designates a gas turbine. In the gas turbine 51, there are provided moving blades 21, 22, 23 on a periphery of a rotor 30. A high temperature combustion gas is led into a combustion gas passage 52 to flow therethrough to rotate the moving blades 21, 22, 23 between stationary blades 43, 44, 45 on a stationary side and to thereby rotate the rotor 30.
In a rotor disc 31, there are provided steam passages 33, 32, which connect to each other and pass through the rotor disc 31 in an axial direction thereof. The steam passages 33, 32 are provided in plural pieces along a circumferential direction of the rotor 30. Cooling steam 80 is led into the steam passage 33 via a steam inlet 35 of a shaft 34 to flow through the steam passage 32 and to enter a cavity 36. It then enters the moving blade 22 of the second stage via a supply side passage 37 for cooling of the blade and, after having cooled the blade, the steam flows into a cavity 39 via a recovery side passage 38. On the other hand, the steam flowing in the steam passage 32 enters a supply side passage 41 via a cavity 40 to flow therefrom into the moving blade 21 of the first stage for cooling the blade and, after having cooled the blade, the steam flows into the cavity 39 via a recovery side passage 42 to be joined with the recovery steam which has come out of the moving blade 22 of the second stage. The steam, so joined, flows out into a cavity 60 to flow through a central portion of the rotor 30 and to be recovered in the shaft 34 portion. Also, a portion of the steam in the steam passage 32 flows through a cavity 61 to be supplied into the compressor 50 for cooling thereof.
As many combined cycle power plants are now being constructed with a need for a high temperature and high efficiency, a gas turbine using a steam-cooled system as mentioned above is being eagerly studied to be employed in place of an air-cooled system as a leading cooling system of the gas turbine. Especially in the combined cycle power plant, a portion of the steam generated at a steam turbine is extracted to be led into the gas turbine for cooling thereof. The steam, used for cooling and being temperature-elevated, is recovered to be further returned to the steam turbine side. Hence an effective use of heat is carried out so as to contribute to a higher efficiency of the power plant. Great attention is being paid thereto recently.
In the gas turbine using the representative steam-cooled system in the prior art as mentioned above, the steam extracted from the steam turbine side is led into the moving blade for cooling thereof via the plurality of the steam passages provided in the periphery of the rotor and via the disc. The steam which has been used for cooling which is temperature-elevated is led into the central portion of the rotor via the cavity to be recovered through the rotor central portion, and then the steam is returned to the steam turbine side to be made use of effectively.
In the above-mentioned prior art steam-cooled system, however, because a low temperature high pressure steam is supplied through the rotor periphery, there are many places from where the steam, while being supplied, leaks to the outside low pressure side through joint portions etc. Hence it is necessary to provide a lot of seal portions. Thus, it has been a large problem in the steam-cooled system as to how the supply steam on the high pressure side is prevented from leaking to the low pressure side.